Peripheral rewinding machines are provided with three rollers with axes parallel to each other and perpendicular to the paper feeding direction, the paper being provided with a series of transverse piercing and weakening lines spaced apart according to regular intervals along the longitudinal development thereof. Two winding rollers, upper and lower, are supported on the frame and cooperate in winding with a third swinging roller, or press, which is kept under pressure on a roll being formed, the so-called log.
At the end of the winding of a log, in the so-called exchange step, the continuity of the paper being wound, partially returned on the upper roller, must be interrupted to unload the finished roll through an output opening defined between the lower roller and the third roller and start a new winding on a new core fed, provided with a longitudinal line of glue, within a channel formed between the upper roller and underlying curved elements, called cradles.
According to a first type of known rewinding machines, such as for example the one shown in EP 1 262 434 A2, in the exchange step the paper is interrupted by the action of a stopping element, or pad, which intervenes against the upper winding roller to press the paper against it, in an upstream position with respect to the new core inserted into the cradles. The stop of the paper against the upper roller results in a downstream tensioning thereof and the consequent tearing along a piercing, but also the formation of wrinkles upstream.
Starting a new winding on a core provided with glue should preferably begin in a point of the initial edge following that with wrinkles. A so-called tail is thus created, i.e. a portion of paper between the glue and the initial end of the paper, which is a scrap, not being useful in contributing to the length of the roll. The tail can reach 100-150 mm in length in the worst cases, equal to 1-1.5 tears, where tear means the distance between two successive piercings.
The quality standards that have imposed on the market, however, require the presence of a tail as short as possible, as it is considered an indicator of the product quality, both because it involves less scrap and because the presence of a short tail facilitates a more balanced winding start, thus creating less asymmetry in the roll.
The reduction of wrinkles has been achieved in rewinding machines by changing the intervention position of the stopping element against the upper winding roller. Trying to change the principle of intervention of the mechanical means on the paper, through the provision of mechanical tearing means placed between the paper being wound and the upper roller and acting in a direction oriented from the upper roller outwards, an attempt has been made to totally eliminate the wrinkle formation phenomenon. EP 2 422 943 A1 for example shows a plurality of arms arranged within transverse grooves of the upper winding roller and provided with a pointed end element adapted to protrude with respect to the shell of upper roller to intervene during the exchange step at a piercing of the paper to break the same, acting on the surface of the upper roll outwards, and to return to a retracted rest position during the winding.
However, this machine has some drawbacks that don't make it actually competitive compared to the rewinding machine provided with stopping element. In fact, the presence of a large number of parallel transverse grooves in the upper roller causes permanent marks on the first paper windings, considered by the market a sign of low product quality. Moreover, since the protuberances have to tear the paper during the exchange step along a piercing precisely facing them, the final length of the roll produced can only take certain values closely tied to the length of the piercings and to the development of the upper roller.